physics- energy

Energy

• ability to do work or make things happen

• needed to move or heat something, to make noise or light or to change an object's shape

Kinetic energy

• energy of movement

• Anything that moves has kinetic energy

• the faster an object moves and the heavier an object is, the more of this type of energy it will have

• There are five forms of kinetic energy

light/radiant energy

• Electromagnetic energy that travels in transverse waves

• Light bulbs, a candle flame

thermal/heat energy

• Vibration or movement of particles

• Hot water, a radiator

Electrical Energy

• Energy from flow of an electric charge

• anything that uses electricity

Sound energy

• Vibration transferred through an object/medium in a Longitudinal wave to produce sound

• Talking, music, radio

mechanical energy

• Energy due to motion of an object

• car

Potential energy

• stored energy

• There are four forms of potential energy

elastic potential energy

• energy stored in elastic objects

• elastic objects- any object that can stretch then return to their original shape

• Clockwork toys, a bungee cord

gravitational potential energy

• energy stored in an object’s height

• A book on a high shelf, a parachutist

chemical energy

• Energy stored in bonds of atoms and molecules

• Food, batteries, fuels

nuclear energy

• Energy stored in atoms’ nuclei

• Nuclear bombs and power stations, the sun

kinetic and potential energy interact in a closed energy system

• energy cannot be created or destroyed

• when there is a lot of kinetic energy in an object, there is little potential energy

• when there is a lot of potential energy in an object, there is little kinetic energy

energy transformations

burning match: chemical → light +heat

TV: electrical → light + sound

Catapult: elastic potential → kinetic

torch: chemical → electrical → light

• sometimes there is more than one energy output, we focus on the main energy output/s

• the energy outputs that we don’t want are known as by-products

The Law of Conservation of Energy

• states that energy cannot be created or destroyed, it is just transformed from one form to another.

Energy efficiency

• describes how much of the energy put into a situation is transformed into useful energy.

• Energy that is transformed into waste energy (often sound, heat via friction) cannot be reused.

Compression

Air particles are forced close together

Rarefraction

Less dense region

Longitudinal wave

• Sound travels as one of these waves

• The air particles move back and forth in the same direction as the vibrations pass through the air

Amplitude

• The distance an air particle moves

• A smaller amplitude is a quieter sound

• A larger amplitude is a louder sound

Wavelength

The distance between the start of one compression wave to the start of the next

Frequency

• The number of waves that pass a point each second

• Measure in hertz (Hz)

Short wavelengths

• more vibrations

• Higher frequency

Long wavelengths

• less vibrations

• Lower frequency

Traveling sound

• Sound always needs something to travel through

• It needs a substance or a medium that contains particles that can be compressed to make sound waves

• The medium could be a solid, liquid or a gas

Speed of sound affected by the temperature of the material it is traveling through

• The thermal energy already inside the medium can allow sound to travel faster by adding an extra shove to the sound energy as it is being passed from particle to particle

• It is easier to move the sound energy through a warmed or hot medium because the particles are already vibrating

The speed of sound affected by the closeness of particles and how far they can move

• The closer the particles are to each other, the easier it is for the sound energy to pass to the neighbouring particle

• This allows the sound to move faster through the medium.

• As the particles are closer together in solids than liquids and gases, sound travels faster through solids

Sonar

• Sonar sends out sounds and records how long it takes for the sound to echo or reflect back after striking an object

• The longer the sound takes to return, the further an object is

Transverse waves

• When light waves travel, the vibrations are at right angles to the direction of travel of the wave

Light vs Sound

• Light moves at a speed of 300,000,000 metres per second

• Sound moves at a speed of 340 metres per second

Light waves properties

• Light waves slow down when they travel through water and glass

• Light does not need a medium to travel through due to its electromagnetic nature

Transparent

• Light can pass through a glass window because it has this property

Translucent

• Frosted glass had this property

• It prevents us from seeing through it clearly

Opaque

• Light cannot pass through a material that has this property

• When it is shiny enough, it will reflect light and allow us to see an image

Mirrors

• The normal is an imaginary line that is drawn at 90° to the mirror surface

• The angle of incidence is the angle between the incident ray and the normal

• The angle of reflection is the angle between the reflected ray and the normal

Law of reflection

• The angle of incidence equals the angle of reflection

The virtual image

• When we look into a flat mirror, we see this type of image

• It cannot be touched or projected onto a screen

• The image is always formed where the light rays cross

• The image we see is turned sideways

Convex mirrors

• The centre of the mirror sticks out

• Scatters the light of an object

Concave mirrors

• The centre of the mirror goes in, like a cave

• The reflected light is bent towards a centre point

Refraction

• The bending of light as it passes at an angle from one transparent medium into another

Light travelling towards a more dense medium

• The light travels slower

• Light bends towards the normal

Light travelling towards a less dense medium

• The light travels faster

• Light bends away from the normal

Convex lenses

• causes light rays to converge, or focus

• The focus is the point where the rays cross

• The focal length is the distance from the focus to the middle of the lens

Concave lenses

• causes light rays to diverge, or spread out

• The focus is on the other side of the lens

• The diverging rays are extended back until they pass a certain point

• The focus is described as a virtual focus because the light rays do not really come from this point